Optical display technology continues to evolve competitively. Displays are being developed that are larger, thinner, and yield higher resolutions. Optically addressable displays (“OAD”) allow for larger display sizes while maintaining a minimal amount of circuitry. The circuitry is kept at a minimum because the OAD's pixel elements, which usually contain LEDs activated by receptors, are responsive to light and not electronic signals. The complicated wiring of each pixel that allows it to be activated is eliminated.
The current techniques used to deliver color information to OADs have various drawbacks such as alignment and cost. One technique commonly used is an infrared raster addressing scheme. Each pixel element's color receptor is located and addressed with an IR beam. However, because each receptor is responsive to the IR beam, alignment becomes an issue. The IR beam needs to be precisely aligned to ensure that only the appropriate receptor is addressed at the right time. If the IR beam is misaligned with the color receptors the entire display could shift to an incorrect color set. Additionally, a less severe misalignment could cause the image on the display to exhibit a color shift.
Another technique for delivering color information is frequency modulation. The frequency of the IR beam is varied at the IR source and projected onto the receptor circuits of the pixel elements. The receptor circuits are responsive to one of the varied frequencies of the IR beam. The corresponding pixel is activated only when the receptor receives its varied frequency. Alignment is less of a problem with this technique because each color circuit would be activated only when the correct frequency of the IR beam is received by the receptor. However, this technique is costly and complicated. Every color circuit would have different components resulting in increased costs. The frequency modulation hardware would also increase the cost and complexity on the projector end.
Utilizing different wavelengths of light for each color is also another technique used for delivering color information. A red, green, and blue pixel each includes a receptor that is unique from the other two colored pixels. A different wavelength of light is projected onto the receptors for each of the multiple colors. The receptors contain narrow optical filters that allow the unique selection of the color channels. As with the frequency modulation technique alignment is less of a problem, however, these optical wavelength filters can be very expensive. There remains a need for a cost-efficient optically addressable display system that overcomes the alignment issue.